1. Field of the Invention
The present invention relates to a triplexer circuit for separating an input signal into signals of three frequency bands which are different from each other.
2. Description of the Related Art
Hitherto, there is a duplexer that receives signals of two different frequency bands by a single antenna and separates the signals into the different bands. Such a duplexer is realized by connecting first and second filters 101 and 102 for passing only signals in their bands in parallel with each other as shown in FIG. 20.
In recent years, a triplexer for separating signals of three frequency bands which are different from each other into their bands has been also proposed. In Japanese Patent Laid-Open (JP-A) No. 2003-198309, a triplexer configured by combining filters in multiple stages has been proposed. The triplexer described in JP-A-2003-198309 has a first filter circuit part that passes a signal of a first frequency band and a lowpass filter circuit part connected to the first filter circuit part in parallel with each other and passing a signal of a frequency band lower than the first frequency band. At a post stage of the lowpass filter circuit part, a second filter circuit part that passes a signal of a second frequency band and a third filter circuit part that passes a signal of a third frequency band are connected in parallel.